Systems and Methods of Measuring Temperature in Industrial Environments

ABSTRACT

A temperature detector and method of measuring temperature to obtain temperature readings in environments, such as fluids and gasses, by measuring electrical characteristics of the temperature detector that are influenced by the temperature. The temperature detector can be arranged such that a plurality of measurements can be obtained to provide sufficient diversity and redundancy of the measurements for enhanced diagnostics to be performed, such as optimization for fast dynamic response, calibration stability, in-situ response time testability, and in-situ calibration testability.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 11/156,053,filed on Jun. 8, 2011, which claims the benefit of U.S. ProvisionalPatent Application No. 61/352,544, filed on Jun. 8, 2010.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to temperature sensors, and more particularly, toresistance temperature detectors and diagnostic systems.

2. Description of the Related Art

A Resistance Temperature Detector (“RTD”) is commonly used for sensingthe temperature of an environment by measuring the electricalcharacteristics of the RTD. More specifically, each RTD includescircuitry with electrical characteristics, e.g., resistance, that changedepending on the ambient temperature of the RTD's environment. Therespective relationships between each RTD's electrical characteristicsand the temperature are generally known for each type of RTD.Accordingly, a RTD is selected for a particular application based uponthe RTD's electrical characteristics, the temperatures of theenvironment, the RTD's responsiveness, or another desired factor. Forexample, a RTD can be selected because of its ability to measure extremetemperatures of an industrial process. In some of these industrialenvironments, the temperatures measured by the RTD provide criticaltemperature data used by the process control and safety systems.

BRIEF SUMMARY OF THE INVENTION

A diverse and redundant resistance temperature detector (“D&R RTD”) isdescribed herein and illustrated in the accompanying figures. The D&RRTD is utilized in obtaining temperature readings in environments, suchas fluids and gasses, by measuring electrical characteristics of the D&RRTD that are influenced by the temperature.

The D&R RTD includes a plurality of sensing components configured toundergo largely predictable changes in electrical characteristics wheninfluenced by the D&R RTD's ambient temperature. For example, oneembodiment of the single-element D&R RTD includes four thermocouplewires arranged such that a first pair of thermocouple wires is connectedto a first lead of a sensing element at a first thermocouple junctionfirst and a second pair of the thermocouple wires is connected to a leadof the sensing element at a second thermocouple junction. Thus, thesingle-element D&R RTD includes a total of three temperature sensingcomponents, namely the sensing element, the first thermocouple junction,and the second thermocouple junction, to redundantly measure theenvironment's temperature. For another example, one embodiment of adual-element D&R RTD includes dual sensing elements wherein each sensingelement has a four-wire configuration and two thermocouple junctions.Thus, the dual-element D&R RTD provides six sensing componentmeasurements, namely a first sensing element measurement, twomeasurements for two thermocouple junctions for the first sensingelement, a second sensing element measurement, and two measurements fortwo thermocouple junctions for the second sensing element.

In addition to providing redundancy, the D&R RTD also provides diversityby allowing multiple methods of obtaining measurements to be utilized inmeasuring the electrical characteristics of the sensing element and thethermocouple junctions. For example, in one embodiment, the method ofobtaining measurements from the sensing element is based on RTDtechniques while the method of obtaining measurements from thethermocouple junctions is based on a thermocouple technique.

The D&R RTD's can be arranged such that a plurality of measurements tobe obtained, which provides sufficient diversity and redundancy of themeasurements for enhanced diagnostics to be performed, such asoptimization for fast dynamic response, calibration stability, in-situresponse time testability, and in-situ calibration testability. Otherenhanced diagnostics that can be performed include deriving the D&R RTDtransfer function, and using the D&R RTD measurements to provide inputto a Johnson noise thermometer to measure absolute temperature.

Additional aspects and advantages of the present general inventiveconcept will be set forth in part in the description which follows, and,in part, will be obvious from the description, or may be learned bypractice of the present general inventive concept.

The foregoing and/or other aspects and advantages of the present generalinventive concept may be achieved by a temperature detector including afirst sensing element having a first lead and a second lead, the firstsensing element having a electrical characteristic that varies inresponse to temperature, the electrical characteristic having asubstantially linear variation over a selected temperature range andcorresponding to a first temperature measurement, a first pair ofthermocouple wires connected to the first lead of the first sensingelement at a first thermocouple junction and extending from the firstthermocouple junction to define a first pair of connection points, thefirst thermocouple junction having an electrical characteristic thatvaries in response to temperature, the electrical characteristic havinga substantially linear variation over a selected temperature range andcorresponding to a second temperature measurement, a second pair ofthermocouple wires connected to the second lead of the first sensingelement at a second thermocouple junction and extending from the secondthermocouple junction to define a second pair of connection points, thesecond thermocouple junction having an electrical characteristic thatvaries in response to temperature, the electrical characteristic havinga substantially linear variation over a selected temperature range andcorresponding to a third temperature measurement, a second sensingelement having a first lead and a second lead, the sensing elementhaving a electrical characteristic that varies in response totemperature, the electrical characteristic having a substantially linearvariation over a selected temperature range and corresponding to afourth temperature measurement, a third pair of thermocouple wiresconnected to the first lead of the second sensing element at a firstthermocouple junction and extending from the first thermocouple junctionto define a third pair of connection points, the third thermocouplejunction having an electrical characteristic that varies in response totemperature, the electrical characteristic having a substantially linearvariation over a selected temperature range and corresponding to a fifthtemperature measurement, a fourth pair of thermocouple wires connectedto the second lead of the second sensing element at a secondthermocouple junction and extending from the second thermocouplejunction to define a fourth pair of connection points, the fourththermocouple junction having an electrical characteristic that varies inresponse to temperature, the electrical characteristic having asubstantially linear variation over a selected temperature range andcorresponding to a sixth temperature measurement, and a diagnostic unitconfigured to process the temperature measurements such that the firsttemperature measurement is acquired by measuring the electricalcharacteristic of the first sensing element using one of the first pairof connection points and one of the second pair of connection points,the second temperature measurement is acquired by measuring theelectrical characteristic of the first thermocouple junction using thefirst pair of connection points, the third temperature measurement isacquired by measuring the electrical characteristic of the secondthermocouple junction by using the second pair of connection points, thefourth temperature measurement is acquired by measuring the electricalcharacteristic of the second sensing element using one of the third pairof connection points and one of the fourth pair of connection points,the fifth temperature measurement is acquired by measuring theelectrical characteristic of the third thermocouple junction using thethird pair of connection points, and the sixth temperature measurementby measuring the electrical characteristic of the fourth thermocouplejunction by using the fourth pair of connection points, wherein thediagnostic unit processes the temperature measurements such that thefirst, second, third, fourth, fifth, and sixth temperature measurementsare cross calibrated by determining an average temperature therefor,determining a deviation from the average temperature for each of thefirst, second, third, fourth, fifth, and sixth temperature measurements,and calculating a calibration coefficient for each of the first, second,third, fourth, fifth, and sixth temperature measurements.

The thermocouple wires may pass through an isothermal block thatregulates the thermocouple reference junction to equilibrium therebyminimizing axial heat transfer.

The first through sixth temperature measurements may be calculated togenerate redundancy for cross calibration to enhance diagnostics tooptimize one or more of dynamic response, calibration stability, in-situresponse time testability, and in-situ calibration testability.

The temperature detector may further include a thermowell housing thesensing elements and thermocouple junctions.

The temperature detector may further include a sheath enclosing thesensing element and thermocouple junctions.

The temperature detector may further include an air gap between thesheath and the thermowell to allow for the expansion of materials and toensure that the sensing elements are not damaged.

The temperature detector may further include a thermal coupling compounddisposed in the air gap.

The foregoing and/or other aspects and advantages of the present generalinventive concept may also be achieved by a temperature detectorincluding a sensing element having a first lead and a second lead, thesensing element having a electrical characteristic that varies inresponse to temperature, the electrical characteristic having asubstantially linear variation over a selected temperature range andcorresponding to a first temperature measurement, a first pair ofthermocouple wires connected to the first lead at a first thermocouplejunction and extending from the first thermocouple junction to define afirst pair of connection points, the first thermocouple junction havingan electrical characteristic that varies in response to temperature, theelectrical characteristic having a substantially linear variation over aselected temperature range and corresponding to a second temperaturemeasurement, a second pair of thermocouple wires connected to the secondlead at a second thermocouple junction and extending from the secondthermocouple junction to define a second pair of connection points, thesecond thermocouple junction having an electrical characteristic thatvaries in response to temperature, the electrical characteristic havinga substantially linear variation over a selected temperature range andcorresponding to a third temperature measurement, a thermowell enclosingthe sensing element, the first thermocouple junction and the secondthermocouple junction, and a diagnostic unit configured to process thetemperature measurements such that the first temperature measurement isacquired by measuring the electrical characteristic of the sensingelement using one of the first pair of connection points and one of thesecond pair of connection points, the second temperature measurement isacquired by measuring the electrical characteristic of the firstthermocouple junction using the first pair of connection points, and thethird temperature measurement is acquired by measuring the electricalcharacteristic of the second thermocouple junction by using the secondpair of connection points, wherein the diagnostic unit processes thetemperature measurements such that the first temperature measurement,the second temperature measurement and the third temperature measurementare cross calibrated by determining an average temperature therefor,determining a deviation from the average temperature for each of thefirst temperature measurement and the second temperature measurement andthe third temperature measurement, and calculating a calibrationcoefficient for each of the first temperature measurement and the secondtemperature measurement and the third temperature measurement.

The first temperature measurement may be the electrical resistancebetween one of the first pair of connection points and one of the secondpair of connection points upon a current being supplied thereto.

The thermocouple wires may pass through an isothermal block thatregulates the thermocouple reference junction to equilibrium therebyminimizing axial heat transfer.

The temperature detector may further include a sheath enclosing thesensing element and thermocouple junctions.

The temperature detector may further include an air gap between thesheath and the thermowell to allow for the expansion of materials and toensure that the sensing element is not damaged.

The first, second, and third temperature measurements may be calculatedto generate redundancy for cross calibration to enhance diagnostics tooptimize one or more of dynamic response, calibration stability, in-situresponse time testability, and in-situ calibration testability.

The foregoing and/or other aspects and advantages of the present generalinventive concept may also be achieved by a method of measuringtemperature including measuring a first temperature utilizing a sensingelement having a first lead and a second lead, the sensing elementhaving an electrical characteristic that varies in response totemperature, the electrical characteristic having a substantially linearvariation over a first selected temperature range, measuring a secondtemperature utilizing a first pair of thermocouple wires connected tothe first lead at a first thermocouple junction and extending from thefirst thermocouple junction to define a first pair of connection points,the first thermocouple junction having an electrical characteristic thatvaries in response to temperature, the electrical characteristic havinga substantially linear variation over a second selected temperaturerange, measuring a third temperature utilizing a second pair ofthermocouple wires connected to the second lead at a second thermocouplejunction and extending from the second thermocouple junction to define asecond pair of connection points, the second thermocouple junctionhaving an electrical characteristic that varies in response totemperature, the electrical characteristic having a substantially linearvariation over a third selected temperature range, processing thetemperature measurements such that the first temperature measurement isacquired by measuring the electrical characteristic of the sensingelement using one of the first pair of connection points and one of thesecond pair of connection points, the second temperature measurement isacquired by measuring the electrical characteristic of the firstthermocouple junction using the first pair of connection points, and thethird temperature measurement is acquired by measuring the electricalcharacteristic of the second thermocouple junction by using the secondpair of connection points, and cross-calibrating the first, second andthird temperature measurements by determining an average temperaturetherefor, determining a deviation from the average temperature for eachof the first temperature measurement and the second temperaturemeasurement and the third temperature measurement, and calculatingcalibration coefficients for each of the first temperature measurementand the second temperature measurement and the third temperaturemeasurement.

The method may further include deriving a transfer function for atemperature detector by using a thermocouple junction signal as an inputand a sensing element signal as an output.

Other features and aspects may be apparent from the following detaileddescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The above-mentioned and additional features of the invention will becomemore clearly understood from the following detailed description of theinvention read together with the drawings in which:

FIG. 1 is an illustration of a schematic of one embodiment of a diverseand redundant resistance temperature detector (“D&R RTD”) in athermowell;

FIG. 2 is an illustration of a schematic of one embodiment of a D&R RTD,which has multiple sensing elements, in a thermowell;

FIG. 3 a is an illustration of one configuration of a D&RRTD-in-thermowell assembly;

FIG. 3 b is an illustration of one configuration of a D&RRTD-in-thermowell assembly;

FIG. 4 is an illustration of one embodiment of a D&R RTD configured forradial heat transfer;

FIG. 5 a is an illustration of one embodiment of a D&R RTD-in-thermowellassembly;

FIG. 5 b is an illustration of one embodiment of a D&R RTD-in-thermowellassembly; and

FIG. 6 is an illustration of an alternate embodiment of a D&R RTD.

DETAILED DESCRIPTION OF THE INVENTION

A diverse and redundant resistance temperature detector (“D&R RTD”) isdescribed in detail herein and illustrated in the accompanying figures.The D&R RTD is utilized in obtaining temperature readings inenvironments, such as fluids and gasses, by measuring electricalcharacteristics of the D&R RTD that are influenced by the temperature.Furthermore, the D&R RTD's are arranged such that a plurality ofmeasurements can be obtained, which provides sufficient diversity andredundancy of the measurements for enhanced diagnostics to be performed,such as optimization for fast dynamic response, calibration stability,in-situ response time testability, and in-situ calibration testability.

FIG. 1 illustrates a schematic of one embodiment of a diverse andredundant resistance temperature detector (“D&R RTD”) 10 in a thermowell12. The D&R RTD includes a plurality of sensing components configured toundergo largely predictable changes in electrical characteristics wheninfluenced by the D&R RTD's 10 ambient temperature. In the illustratedembodiment, the D&R RTD 10 includes four thermocouple wires 14 inelectrical communication with a single sensing element 16. As depicted,the D&R RTD 10 includes two pair of the thermocouple wires 14 arrangedin a parallel configuration with the sensing element 16. Specifically, afirst pair of thermocouple wires 18 is connected to a first lead of thesensing element 16 at a first thermocouple junction 20 and a second pairof thermocouple wires 22 is connected to a second lead of the sensingelement 16 at a second thermocouple junction 24. Thus, the D&R RTD 10,depicted in FIG. 1, includes a total of three temperature sensingcomponents, namely the sensing element 16, the first thermocouplejunction 20, and the second thermocouple junction 24, to redundantlymeasure the environment's temperature. It is possible to connect thetemperature detector 10 to a diagnostic unit to combine, process, andcalculate the temperature measurements to provide a diagnostics systemcapable of generating enhanced diagnostics information based onredundancy of the temperature measurements for cross calibration tooptimize one or more of dynamic response, calibration stability, in-situresponse time testability, and in-situ calibration testability of thesystem.

The D&R RTD 10 allows for measuring the electrical characteristics ofeach of these sensing components. Specifically, in one embodiment, theelectrical characteristic of the sensing element 16 is measured betweenone thermocouple wire 14 of the first pair of thermocouple wires 18 andone thermocouple wire 14 of the second pair of thermocouple wires 22.While the electrical characteristic of the first thermocouple junction20 is obtained by measuring the electrical characteristic between thefirst pair of thermocouple wires 18 and the electrical characteristic ofthe second thermocouple junction 24 is obtained by measuring theelectrical characteristic between the second pair of thermocouple wires22.

In addition to providing redundancy, the D&R RTD 10 also providesdiversity by allowing multiple methods of obtaining measurements to beutilized in measuring the electrical characteristics of the sensingelement 16 and the thermocouple junctions 20, 24. Specifically, in oneembodiment, the method of obtaining measurements from the sensingelement 16 is based on RTD techniques while the method of obtainingmeasurements from the thermocouple junctions 20, 24 is based on athermocouple technique. For example, one suitable method to obtainmeasurements from the sensing element 16 is to measure the resistance ofthe sensing element 16 upon a current being supplied thereto. Onesuitable method to obtain measurements from the thermocouple junction20, 24 is to measure the Seebeck voltage of the thermocouple junction20, 24 when the thermocouple junction 20, 24 is subjected to a change intemperature. In the embodiment illustrated in FIG. 1, the Seebeckvoltage measurements are further simplified by passing the thermocouplewires 14 through an isothermal block 26 that regulates the thermocouplereference junction to equilibrium. Thus, the D&R RTD 10 providesredundant measurements through diverse methods to improve thereliability and accuracy of the temperature measurements.

Alternate embodiments of the D&R RTD 10 can include multiple sensingelements 16 and thermocouple junctions 20, 24 to further improve thediversity and redundancy of the temperature measurements.

FIG. 2 illustrates a schematic of one embodiment of a D&R RTD 10, whichhas multiple sensing elements, in a thermowell 12. In the illustratedembodiment, the D&R RTD 10 includes dual sensing elements 16 a, 16 bwherein each sensing element 16 a, 16 b has a four-wire thermocouple 14configuration and two thermocouple junctions 20 a, 20 b, 20 c, 20 d.Thus, the D&R RTD 10 with dual sensing elements provides six sensingcomponents 16 a, 16 b, 20 a, 20 b, 20 c, 20 d that measure the sametemperature. These six measurements include one measurement for thefirst sensing element 16 a, two measurements for the thermocouplejunctions 20 a, 24 a for the first sensing element 16 a, one measurementfor the second sensing element 16 b, and two measurements for thethermocouple junctions 20 b, 24 b for the second sensing element 16 b.Moreover, the D&R RTD 10 with dual sensing elements 16 a, 16 b continuesto use two different techniques to measure the ambient temperature,thereby maintaining diversity while increasing the redundancy of themeasurements.

As mentioned above, the D&R RTD 10 is arranged such that the pluralityof measurements provides sufficient diagnostics. For example, the D&RRTD 10 is configured to allow traditional and in-situ calibrationtesting to be performed on the D&R RTD 10. Calibration testing providesan indication of whether a sensing element 16 or a thermocouple junction20, 24 is faulty, and also whether a sensing element 16 or thethermocouple junction 20, 24 is deviating from a linear relationshipwith the temperature. The cross calibration technique is one method forverifying calibration on the D&R RTD 10. Generally, cross calibrationincludes obtaining measurements from the D&R RTD 10, determining theaverage temperature, determining deviations there from, and determiningcalibration coefficients for the deviating measurements of the D&R RTD10. For the cross calibration technique, it is important to obtain atleast three measurements of the same temperature, from one or more D&RRTDs 10, in order to obtain accurate calibration information. Forexample, the D&R RTD 10 with dual sensing elements 16 a, 16 b providessix measurements for cross calibration wherein the redundantmeasurements are analyzed for determination of whether the measurementsare in conformance with one another. It should be noted that crosscalibration can be performed provided that the D&R RTD 10 does notexperience a common mode effect that influences or skews themeasurements similarly. This assumption can be generally acceptedbecause the D&R RTD 10 is fault tolerant and essentially immune fromcommon mode failures. Again, because the D&R RTD 10 measurements areobtained from two sources, namely the sensing element and thethermocouple junctions 20, 24, and because the measurements are obtainedthrough different methods, it is highly unlikely that the D&R RTD 10will experience common mode failures for all the sources ofmeasurements. Furthermore, the D&R RTD 10 with dual sensing elements 16a, 16 b is configured for fault tolerance to insure that accuratemeasurements are still obtainable when conventional RTDs normally sufferfrom cold working due to vibration.

The D&R RTD 10 also allows for additional enhanced diagnostics to beperformed. For example, a D&R RTD 10 transfer function can be derivedusing the thermocouple junction signal as input and the sensing elementsignal as output. Additionally, if additional temperature information isdesired, the D&R RTD 10 measurements can serve to provide input to aJohnson noise thermometer to measure absolute temperature.

FIGS. 3 a and 3 b illustrate two configurations of a D&RRTD-in-thermowell assembly 28. For demonstrative purposes, a D&R RTD 10having a single sensing element 16 is shown housed within a flat-tipthermowell 12 a in FIG. 3 a and a tapered-tip thermowell 12 b in FIG. 3b. One consideration in selecting the shape of the thermowell 12 is theamount and types of static and dynamic forces in the environment forwhich the D&R RTD 10 is selected. As shown in FIGS. 3 a and 3 b, the D&RRTD-in-thermowell assembly 28 also includes an air gap 30 and a sheath32. The thermowell 28, the air gap 30, and the sheath 32 protect the D&RRTD 10 from damage by isolating the D&R RTD 10 from direct contact withthe environment; however, this protection also insulates the D&R RTD 10and slows down the response time. The response time is the amount oftime it takes the temperature sensor to observe the change intemperature. Although the quickest manner of heat transfer between thethermowell 12 and D&R RTD 10 occurs when there is contact there between,the expansion of materials often results in damage to the sensingelement 16. Accordingly, an air gap is necessary to allow for theexpansion of materials and to ensure that the D&R RTD 10 is not damaged.

FIG. 4 illustrates one embodiment of the D&R RTD-in-thermowell assembly28 configured to promote the radial heat transfer and reduce axial heattransfer. By reducing axial heat transfer, the D&R RTD 10 providesadditional enhanced diagnostics. A brief discussion of the embodimentillustrated in FIG. 4 will aid in the understanding of why theseadditional diagnostics are available. In FIG. 4, the D&RRTD-in-thermowell assembly 28 includes a tapered-tip thermowell 12 and aD&R RTD 10. The D&R RTD 10 includes a wire-wound sensing element 16,namely a wire 34 wound around a mandrel 36 made of an electricallyinsulating material. The materials utilized in the D&R RTD 10 dependupon the minimum and maximum temperatures of the environment and thedegree of linearity between the D&R RTD's 10 electrical characteristicsand these minimum and maximum temperatures. For example, a suitableselection for a wire-wound sensing element 16, which is subjected tohigh temperatures in industrial processes, includes a platinum wire 34secured on an Al₂O₃ or MgO mandrel 36. The D&R RTD-in-thermowellassembly 28 also includes insulation to inhibit axial heat transfer andpromote radial heat transfer for the sensing element. More specifically,the insulation is packed above the sensing element to keep the heat atthe tip and minimizing axial heat transfer. Thus, the D&R RTD 10 isisolated from other environments (such as the environment where thethermocouple wires extend) such that the D&R RTD 10 is predominatelyinfluenced by the environment's temperature with minimal dissipation.Thus, the D&R RTD's 10 measurements substantially reflect thetemperature of the environment.

As mentioned above, the D&R RTD-in-thermowell assembly 28 configured topromote the radial heat transfer and reduce axial heat transfer allowsadditional diagnostics to be performed. For example, the D&R RTD 10allows for in-situ response time testing. One suitable method ofperforming in-situ response time testing is the loop current stepresponse (“LCSR”) technique. LCSR testing measures the response time ofthe D&R RTD 10 under process operating conditions. For example, asuitable response time for the D&R RTD-in-thermowell assembly 28 is aresponse time of less than 5 s in a fluid with a flow rate of 1 m/s.

In addition to response time, the D&R RTD 10 allows for enhanceddiagnostics and monitoring of the air gap 30 between the sensing element16 and the thermowell 12. LCSR is also one suitable method ofdetermining the distance of the air gap 30. It should be noted that theLCSR testing provides an indication of the distance as it exists at thepresent temperature. Accordingly, based upon the LCSR results, the D&RRTD-in-thermowell assembly 28 is selectable such that a particular D&RRTD 10 optimizes the air gap 30. Specifically, the D&R RTD 10 having adesired air gap 30 is selected based on previous measurements at thetemperature such that the D&R RTD-in-thermowell 28 is optimized toprovide the quickest response time while still providing a sufficientair gap 30 for thermal expansion. Thus, the enhanced diagnostics allowthe D&R RTD 10 to be selected for optimization of the system.

Furthermore, LCSR testing also provides for differentiation betweenproblems experienced by the sensing element 16 or thermocouple junctions20, 24 and problems which are experienced by a cable or connector. Thatis, if the D&R RTD 10 signal becomes anomalous, one can diagnose whetherthe problem is in the D&R RTD 10 or in the cables and connectors betweenthe D&R RTD 10 and the instrumentation cabinets.

FIGS. 5 a and 5 b illustrate two embodiments of a D&R RTD-in-thermowellassembly 28. More specifically, the depicted D&R RTD-in-thermowellassemblies 28 include a flat tipped thermowell with plating (FIG. 5 a),and a tapered tip thermowell with plating (FIG. 5 b). The D&RRTD-in-thermowell assemblies 28, of FIGS. 5 a -5 d, further include athermal coupling compound 38 that occupies the area between the sheath32 and inside wall of the thermocouple 12, thereby replacing the airgap. The thermal coupling compound 38 produces an accelerated dynamicresponse while allowing for the expansion of materials. Additionally,the D&R RTD-in-thermowell assemblies 28, include plating 40 that furtheraccelerates the dynamic response. Alternate embodiments of the D&RRTD-in-thermowell assembly can include any other desired configurationwith a suitable response time.

FIG. 6 illustrates an alternate embodiment of a D&R RTD 10. In someapplications that necessitate a faster response time than can beachieved using the D&R RTD-in-thermowell 28, a wet-type D&R RTD 10 canbe used. A wet-type D&R RTD 10 omits the thermowell and uses materialsselected to improve the expected lifespan and performancecharacteristics (e.g., linearity, temperature range) of the wet-type D&RRTD 10 based on the environmental conditions for which it is designed.For example, in the illustrated embodiment, the D&R RTD 10 includes asensing element 16 and two thermocouple junctions 20, 24 enclosed withina sheath 32. Factors that affect the expected lifespan and performanceinclude thermal expansion, stress and strain, and corrosion of thecomponents. One suitable selection for the wet-type D&R RTD 10 is aplatinum sensing element with Type K (chromel-alumel) thermocouples.

While the present invention has been illustrated by description ofseveral embodiments and while the illustrative embodiments have beendescribed in considerable detail, it is not the intention of theapplicant to restrict or in any way limit the scope of the appendedclaims to such detail. Additional advantages and modifications willreadily appear to those skilled in the art. The invention in its broaderaspects is therefore not limited to the specific details, representativeapparatus and methods, and illustrative examples shown and described.Accordingly, departures may be made from such details without departingfrom the spirit or scope of applicant's general inventive concept.

1. A temperature detector comprising: a first sensing element having afirst lead and a second lead, said first sensing element having aelectrical characteristic that varies in response to temperature, saidelectrical characteristic having a substantially linear variation over aselected temperature range and corresponding to a first temperaturemeasurement; a first pair of thermocouple wires connected to said firstlead of said first sensing element at a first thermocouple junction andextending from said first thermocouple junction to define a first pairof connection points, said first thermocouple junction having anelectrical characteristic that varies in response to temperature, saidelectrical characteristic having a substantially linear variation over aselected temperature range and corresponding to a second temperaturemeasurement; a second pair of thermocouple wires connected to saidsecond lead of said first sensing element at a second thermocouplejunction and extending from said second thermocouple junction to definea second pair of connection points, said second thermocouple junctionhaving an electrical characteristic that varies in response totemperature, said electrical characteristic having a substantiallylinear variation over a selected temperature range and corresponding toa third temperature measurement; a second sensing element having a firstlead and a second lead, said sensing element having a electricalcharacteristic that varies in response to temperature, said electricalcharacteristic having a substantially linear variation over a selectedtemperature range and corresponding to a fourth temperature measurement;a third pair of thermocouple wires connected to said first lead of saidsecond sensing element at a first thermocouple junction and extendingfrom said first thermocouple junction to define a third pair ofconnection points, said third thermocouple junction having an electricalcharacteristic that varies in response to temperature, said electricalcharacteristic having a substantially linear variation over a selectedtemperature range and corresponding to a fifth temperature measurement;a fourth pair of thermocouple wires connected to said second lead ofsaid second sensing element at a second thermocouple junction andextending from said second thermocouple junction to define a fourth pairof connection points, said fourth thermocouple junction having anelectrical characteristic that varies in response to temperature, saidelectrical characteristic having a substantially linear variation over aselected temperature range and corresponding to a sixth temperaturemeasurement; and a diagnostic unit configured to process saidtemperature measurements such that said first temperature measurement isacquired by measuring the electrical characteristic of said firstsensing element using one of said first pair of connection points andone of said second pair of connection points, said second temperaturemeasurement is acquired by measuring the electrical characteristic ofsaid first thermocouple junction using said first pair of connectionpoints, said third temperature measurement is acquired by measuring saidelectrical characteristic of said second thermocouple junction by usingsaid second pair of connection points, said fourth temperaturemeasurement is acquired by measuring the electrical characteristic ofsaid second sensing element using one of said third pair of connectionpoints and one of said fourth pair of connection points, said fifthtemperature measurement is acquired by measuring the electricalcharacteristic of said third thermocouple junction using said third pairof connection points, and said sixth temperature measurement bymeasuring said electrical characteristic of said fourth thermocouplejunction by using said fourth pair of connection points; wherein thediagnostic unit processes said temperature measurements such that saidfirst, second, third, fourth, fifth, and sixth temperature measurementsare cross calibrated by determining an average temperature therefor,determining a deviation from the average temperature for each of thefirst, second, third, fourth, fifth, and sixth temperature measurements,and calculating a calibration coefficient for each of the first, second,third, fourth, fifth, and sixth temperature measurements.
 2. Thetemperature detector of claim 1, wherein said thermocouple wires passthrough an isothermal block that regulates the thermocouple referencejunction to equilibrium thereby minimizing axial heat transfer.
 3. Thetemperature detector of claim 1, wherein said first through sixthtemperature measurements are calculated to generate redundancy for crosscalibration to enhance diagnostics to optimize one or more of dynamicresponse, calibration stability, in-situ response time testability, andin-situ calibration testability.
 4. The temperature detector of claim 1,further comprising a thermowell housing the sensing elements andthermocouple junctions.
 5. The temperature detector of claim 4, furthercomprising a sheath enclosing the sensing element and thermocouplejunctions.
 6. The temperature detector of claim 5, further comprising anair gap between the sheath and said thermowell to allow for theexpansion of materials and to ensure that the sensing elements are notdamaged.
 7. The temperature detector of claim 6, further comprising athermal coupling compound disposed in the air gap.
 8. A temperaturedetector comprising: a sensing element having a first lead and a secondlead, said sensing element having a electrical characteristic thatvaries in response to temperature, said electrical characteristic havinga substantially linear variation over a selected temperature range andcorresponding to a first temperature measurement; a first pair ofthermocouple wires connected to said first lead at a first thermocouplejunction and extending from said first thermocouple junction to define afirst pair of connection points, said first thermocouple junction havingan electrical characteristic that varies in response to temperature,said electrical characteristic having a substantially linear variationover a selected temperature range and corresponding to a secondtemperature measurement; a second pair of thermocouple wires connectedto said second lead at a second thermocouple junction and extending fromsaid second thermocouple junction to define a second pair of connectionpoints, said second thermocouple junction having an electricalcharacteristic that varies in response to temperature, said electricalcharacteristic having a substantially linear variation over a selectedtemperature range and corresponding to a third temperature measurement;a thermowell enclosing said sensing element, said first thermocouplejunction and said second thermocouple junction; and a diagnostic unitconfigured to process said temperature measurements such that said firsttemperature measurement is acquired by measuring the electricalcharacteristic of said sensing element using one of said first pair ofconnection points and one of said second pair of connection points, saidsecond temperature measurement is acquired by measuring the electricalcharacteristic of said first thermocouple junction using said first pairof connection points, and said third temperature measurement is acquiredby measuring said electrical characteristic of said second thermocouplejunction by using said second pair of connection points; wherein thediagnostic unit processes said temperature measurements such that saidfirst temperature measurement, said second temperature measurement andsaid third temperature measurement are cross calibrated by determiningan average temperature therefor, determining a deviation from theaverage temperature for each of the first temperature measurement andthe second temperature measurement and the third temperaturemeasurement, and calculating a calibration coefficient for each of thefirst temperature measurement and the second temperature measurement andthe third temperature measurement.
 9. The temperature detector of claim8, wherein said first temperature measurement is the electricalresistance between one of said first pair of connection points and oneof said second pair of connection points upon a current being suppliedthereto.
 10. The temperature detector of claim 8, wherein saidthermocouple wires pass through an isothermal block that regulates thethermocouple reference junction to equilibrium thereby minimizing axialheat transfer.
 11. The temperature detector of claim 8, furthercomprising a sheath enclosing the sensing element and thermocouplejunctions.
 12. The temperature detector of claim 11, further comprisingan air gap between the sheath and said thermowell to allow for theexpansion of materials and to ensure that the sensing element is notdamaged.
 13. The temperature detector of claim 8, wherein said first,second, and third temperature measurements are calculated to generateredundancy for cross calibration to enhance diagnostics to optimize oneor more of dynamic response, calibration stability, in-situ responsetime testability, and in-situ calibration testability.
 14. A method ofmeasuring temperature comprising: measuring a first temperatureutilizing a sensing element having a first lead and a second lead, saidsensing element having an electrical characteristic that varies inresponse to temperature, said electrical characteristic having asubstantially linear variation over a first selected temperature range;measuring a second temperature utilizing a first pair of thermocouplewires connected to said first lead at a first thermocouple junction andextending from said first thermocouple junction to define a first pairof connection points, said first thermocouple junction having anelectrical characteristic that varies in response to temperature, saidelectrical characteristic having a substantially linear variation over asecond selected temperature range; measuring a third temperatureutilizing a second pair of thermocouple wires connected to said secondlead at a second thermocouple junction and extending from said secondthermocouple junction to define a second pair of connection points, saidsecond thermocouple junction having an electrical characteristic thatvaries in response to temperature, said electrical characteristic havinga substantially linear variation over a third selected temperaturerange; processing said temperature measurements such that said firsttemperature measurement is acquired by measuring said electricalcharacteristic of said sensing element using one of said first pair ofconnection points and one of said second pair of connection points, saidsecond temperature measurement is acquired by measuring said electricalcharacteristic of said first thermocouple junction using said first pairof connection points, and said third temperature measurement is acquiredby measuring said electrical characteristic of said second thermocouplejunction by using said second pair of connection points; andcross-calibrating the first, second and third temperature measurementsby determining an average temperature therefor, determining a deviationfrom the average temperature for each of the first temperaturemeasurement and the second temperature measurement and the thirdtemperature measurement, and calculating calibration coefficients foreach of said first temperature measurement and said second temperaturemeasurement and said third temperature measurement.
 15. The method ofclaim 14, further comprising deriving a transfer function for atemperature detector by using a thermocouple junction signal as an inputand a sensing element signal as an output.